Exploiting the Natural Motion of a SCARA-Like Manipulator for Pick-and-Place Tasks

The paper discusses the exploitation of the natural motion of a SCARA-like manipulator to reduce energy consumption in pick-and-place tasks. The considered architecture is derived from a classical SCARA robot (RRPR) by substituting the prismatic joint with a four-bar mechanism, obtaining the RR-4R-R scheme. When a torsional spring is added to one of the revolute joints of the four-bar for elastic balancing, a natural motion of the end-effector in the vertical plane arises, which can be exploited to reduce energy consumption in repetitive pick-and-place tasks. A multibody model of the manipulator has been employed to compare the energy consumption in case of no balancing (WB), elastic balancing by means of a linear spring with exploitation of the natural motion (NB), and exact elastic balancing (indifferent equilibrium) by means of a zero free-length spring (EB). Simulation results indicate that EB overperforms NB for slow motions, while NB is favorable for fast cyclic motions, providing an estimation of the convenience threshold between the two approaches, and indicating that the proposed manipulator can replace the widespread SCARA architecture, remarkably improving the energy efficiency of many robotized lines.